1. Field of the Invention
This invention relates generally to methods and apparatus for drilling and completing subterranean wells and, more particularly, to methods and apparatus for a drillable bridge plug, frac plug, cement retainer, and other related downhole apparatus, including apparatus for running these downhole apparatus.
2. Description of Related Art
There are many applications in well drilling, servicing, and completion in which it becomes necessary to isolate particular zones within the well. In some applications, such as cased-hole situations, conventional bridge plugs such as the Baker Hughes model T, N1, NC1, P1, or S wireline-set bridge plugs are inserted into the well to isolate zones. The bridge plugs may be temporary or permanent; the purpose of the plugs is simply to isolate some portion of the well from another portion of the well. In some instances perforations in the well in one portion need to be isolated from perforations in another portion of the well. In other situations there may be a need to use a bridge plug to isolate the bottom of the well from the wellhead. There are also situations where these plugs are not used necessarily for isolation but instead are used to create a cement plug in the wellbore which may be used for permanent abandonment. In other applications a bridge plug with cement on top of it may be used as a kickoff plug for side-tracking the well.
Bridge plugs may be drillable or retrievable. Drillable bridge plugs are typically constructed of a brittle metal such as cast iron that can be drilled out. One typical problem with conventional drillable bridge plugs is that without some sort of locking mechanism, the bridge plug components tend to rotate with the drill bit, which may result in extremely long drill-out times, excessive casing wear, or both. Long drill-out times are highly undesirable as rig time is typically charged for by the hour.
Another typical problem with conventional drillable plugs is that the conventional metallic construction materials, even though brittle, are not easy to drill through. The plugs are generally required to be quite robust to achieve an isolating seal, but the materials of construction may then be difficult to drill out in a reasonable time. These typical metallic plugs thus require that significant weight be applied to the drill-bit in order to drill the plug out. It would be desirable to create a plug that did not require significant forces to be applied to the drill-bit such that the drilling operation could be accomplished with a coiled tubing motor and bit; however, conventional metallic plugs do not enable this.
In addition, when several plugs are used in succession to isolate a plurality of zones within the wellbore, there may be significant pressures on the plug from either side. It would be desirable to design an easily drilled bridge plug that is capable of holding high differential pressures on both sides of the plug. Also, with the potential for use of multiple plugs in the same wellbore, it would be desirable to create a rotational lock between plugs. A rotational lock between plugs would facilitate less time-consuming drill outs.
Additionally, it would be desirable to design an easily drillable frac plug that has a valve to allow fluid communication through the mandrel. It would be desirable for the valve to allow fluid to flow in one direction (e.g. out of the reservoir) while preventing fluid from flowing in the other direction (into the reservoir). It is also desired to design an easily drillable cement retainer that includes a mandrel with vents for circulating cement slurry through the tool.
It is also desired to provide a wire line adapter kit that will facilitate the running of the drillable downhole tool, but still be releasable from the tool. Once released, the wire line adapter kit should be retrievable thus allowing the downhole tool to be drilled. Preferably, the wire line adapter kit should leave little, if any, metal components downhole, thus reducing time milling and/or drilling time to remove plugs.
Additionally, in some downhole operations, it is desirable that a downhole tool function as a bridge plug for some period of time to plug the hole, and subsequently operate as a frac plug or cement retainer which controls fluid flow through the tool. For these applications, a bridge plug is set which prevents fluid flow therethrough, the bridge plug is removed, and subsequently a frac plug or cement retainer is set for controlling fluid flow therethrough. Prior art downhole tools do not allow the same tool to be converted from a bridge plug to a frac plug. Prior art bridge plugs therefore must be removed, either by drilling or milling them out or by retrieving them to the surface, and subsequently setting the frac plug or cement retainer downhole. Not only does this require two tools, but the time required to remove the bridge plug and set the frac plug or cement retainer may be costly to the operation.
Therefore, in one embodiment of the present invention, a downhole tool is described that can selectively operate as a bridge plug in some instances and subsequently act as a frac plug or cement retainer in others, without the need for setting two tools or removing the first before setting the second.
Further, in typical downhole operations, the frac plug is removed. It has been discovered that when it is desired to remove the prior art frac plugs or cement retainers, the flapper may tend to rotate within the mandrel with the mill or drill bit, thus increasing the removal time. Typical frac plugs are hinged within the mandrel. Once the hinge is milled or drilled out in these prior art flappers, the flapper is free to rotate with the drill bit or mill within the mandrel, thus making the remainder of the removal of the flapper time-intensive. Therefore, it is desirable to provide a downhole tool which is easily removed by milling or drilling, in which the flapper does not rotate with the mill or drill during removal.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.